Motor generator unit with multiplexed output

ABSTRACT

A vehicle includes an engine, transmission, auxiliary and high-voltage electrical loads, a drivetrain, and an electrical system. The electrical system, characterized by an absence of a DC-DC converter, includes a full-bridge active rectifier/inverter, a semi-active auxiliary rectifier, an MGU connected to the engine via the drivetrain, and a controller. The controller executes a first operating mode in which the bridge rectifier is disabled and the MGU operates as a motor to restart or assist the engine, and a second operating mode in which the MGU is a generator, with the rectifier/inverter powering the HV-ESS and HV electrical load. The auxiliary rectifier provides an auxiliary DC output voltage to the LV-ESS and auxiliary electrical load. Switches may be positioned between a DC bus connection point and the HV-ESS and LV-ESS, with a switch closed and another opened in the first operating mode, and vice versa in the second operating mode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. patent application Ser. No.14/208,484, filed on Mar. 13, 2014, which is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a motor generator unit having amultiplexed output.

BACKGROUND

Hybrid electric powertrains typically have engine autostop functionalityin which a controller shuts off a fuel feed to an internal combustionengine during idle conditions in order to maximize fuel economy. Abelted alternator starter (BAS) system may be used in conjunction withor in lieu of an auxiliary starter motor to quickly restart the engineafter the autostop event, or to assist the engine during specificoperating conditions to increase torque into or from a transmission. Ina BAS system, a high-voltage motor-generator unit (MGU) is operativelyconnected to a crankshaft of the engine via pulleys and a chain or belt.Motor torque from the MGU cranks and starts the engine during an engineautostart event. Motor torque from the MGU in some BAS systems may alsobe used to selectively assist output torque from the engine in anelectrical assist mode.

The MGU of a BAS system suitable for a wide range of engines istypically rated for voltages higher than 12-15 VDC auxiliary levels soas to minimize operating current. A higher-voltage battery is thus usedfor powering the MGU and other higher-voltage electrical devices such aspositive temperature coefficient (PTC) heaters, coolant pumps, activechassis control devices, and the like. A separate lower-voltageauxiliary battery is used to run various motor vehicle accessories suchas headlights, heating, ventilation, and air conditioning (HVAC)devices, auxiliary motors, and entertainment system components. Theauxiliary battery may be recharged in some configurations via a DC-DCconverter, a device which reduces an output voltage of thehigher-voltage battery to suitable auxiliary voltage levels.

SUMMARY

A vehicle is disclosed herein having an internal combustion engine, atransmission that is connected to the engine, and an electrical systemhaving a controller. The electrical system also includes a polyphasemotor generator unit (MGU), a polyphase full-bridge activerectifier/inverter, a polyphase semi-active auxiliary rectifier, ahigh-voltage energy storage system (HV-ESS), and anauxiliary/low-voltage energy storage system (LV-ESS), with“high-voltage” referring to voltage levels in excess of auxiliaryvoltage levels. The electrical system, in all of the embodimentsdisclosed herein, is characterized by an absence of a conventional DC-DCconverter of the type noted above. While a three-phase MGU is describedhereinafter for illustrative consistency, any polyphase electric machinemay be used within the intended inventive scope.

The controller, via switching commands, controls the full-bridge activerectifier/inverter, i.e., selectively activates the gates of internalsemiconductor switches of the active rectifier/inverter, to therebycontrol the MGU as either a generator or a motor as needed. Control ofthe MGU is powered via energy from the HV-ESS, e.g., a 16-48 VDCmulti-cell rechargeable lithium ion battery or an ultra-capacitor.

In addition to the active rectifier/inverter, the phase windings of theMGU in one embodiment are also connected to the semi-active auxiliaryrectifier. While motoring or when regenerating the LV-ESS, thesemi-active rectifier is controlled to output a lower DC output voltagethan that of the HV-ESS. The voltage output of the semi-active rectifieris connected to the LV-ESS, e.g., a 12 VDC lead acid, lithium ion, orother energy storage device, that supports the vehicle's auxiliaryelectrical load when the vehicle engine is stopped, with the electricalload possibly including a 12 VDC auxiliary starter motor. Such a startermotor may be used for engine cold cranking, and may act as a backupstarting source to a belted alternator starter (BAS) system after anengine autostop event.

In another powertrain operating mode, the MGU may be operated via thecontroller in the capacity of a motor to thereby output torque forrestarting or assisting the engine. This occurs using the voltage outputof the full-bridge active rectifier/inverter, which in the motoring modeis operated solely as an inverter. This action supplies high-voltage ACpower to the phase windings of the MGU. During an engine autostart ortorque assist event, the semi-active bridge rectifier may be temporarilydisabled by the controller so as to enable delivery of a maximum amountof starting torque to the crankshaft, thereby achieving a rapid enginerestart or torque assist.

In other embodiments, solid state switches or semiconductor switches areused to block the flow of electrical current to the DC bus connected toeither the HV-ESS or the LV-ESS, with the particular actived switchdepending on the desired operating mode. The semi-active auxiliaryrectifier may be dispensed with when the switches are used. The switchesmay have a relatively fast switching speed, for instance of less than 1ms in a non-limiting example embodiment, with one switch connecting theoutput of the full-bridge active rectifier/inverter to the positive sideof a high-voltage DC bus and another switch connecting the samerectifier/inverter to the positive side of a low-voltage DC bus.

When regenerating the HV-ESS in this particular embodiment, a firstswitch disposed between the active rectifier/inverter and the HV-ESS isclosed and a second switch disposed between the activerectifier/inverter and the LV-ESS is opened, with this accomplished viatransmission of switching signals to the switches from the controller.To regenerate the LV-ESS, the opposite switching states are commanded bythe controller, i.e., the first switch is opened and the second switchis closed. Excitation of the MGU may be increased via the controllerduring regeneration of the HV-ESS, such as by increasing the fieldcurrent or magnetic flux current of the MGU and decreasing the same,during regeneration of the LV-ESS.

In a non-limiting example embodiment, the vehicle may include aninternal combustion engine having a crankshaft, a transmission having aninput shaft that is connected to the crankshaft, an auxiliary electricalload, and an electrical system. The electrical system may include anHV-ESS, an LV-ESS that is electrically connected to an auxiliaryelectrical load of the vehicle, a polyphase full-bridge activerectifier/inverter, a polyphase semi-active auxiliary rectifier, apolyphase MGU, and a controller. The MGU is electrically connected tothe HV-ESS via the active rectifier/inverter, and to the LV-ESS via thesemi-active auxiliary rectifier.

The controller in this embodiment includes a processor and memory onwhich is recorded instructions for controlling the electrical system toestablish a plurality of powertrain operating modes, i.e., a firstoperating mode and a second operating mode. In the first operating mode,the MGU is operated as a motor for restarting or assisting the engineusing an output of the full-bridge active rectifier/inverter to supplyAC power to windings of the MGU and the semi-active bridge rectifier istemporarily disabled. In the second operating mode, the MGU is operatedvia signals from the controller as a generator, where output of thefull-bridge active rectifier/inverter is controlled to supply DC powerto the HV-ESS and the semi-active bridge rectifier is controlled, alsovia signals from the controller, to provide an auxiliary DC outputvoltage to the LV-ESS and the auxiliary electrical load.

The auxiliary electrical load may include an auxiliary starter motor,and the full-bridge active rectifier/inverter may include a plurality ofmetal-oxide semiconductor field effect transistors (MOSFETs) or othersemiconductor switches. The semi-active auxiliary rectifier may includea plurality of diodes and a plurality of solid state AC switches incommunication with the controller, i.e., switches capable of blockingvoltage of either polarity when commanded off. Example alternative solidstate AC switches include thyristors and back-to-back connected MOSFETs.

The active rectifier/inverter and the semi-active auxiliary rectifierare electrically connected to different turns of the windings of the MGUin another optional embodiment. Additionally, the HV-ESS and the LV-ESSmay be housed or packaged together in a common battery housing.Likewise, the MGU may have a single frame, and the activerectifier/inverter and the semi-active auxiliary rectifier may be housedwithin the single frame.

In another embodiment, a vehicle includes an internal combustion enginehaving a crankshaft, a transmission having an input shaft that isconnected to the crankshaft, an auxiliary electrical load, and anelectrical system. The electrical system includes an HV-ESS, an LV-ESSthat is electrically connected to the auxiliary electrical load, and apolyphase full-bridge active rectifier/inverter having a DC busconnection point, i.e., a physical electrical connection to a DC bus.The electrical system also includes a first switch positioned betweenthe DC bus connection point and the HV-ESS, a second switch positionedbetween the DC bus connection point and the LV-ESS, a polyphase MGU thatis electrically connected to AC bus connection points of the activerectifier, and a controller.

The controller in this embodiment has a processor and memory on which isrecorded instructions for controlling the electrical system to establisha plurality of powertrain operating modes. Execution of the instructionsby the processor causes the controller to establish a first operatingmode or a second operating mode. In the first operating mode, the firstswitch is closed and the second switch is opened, via switching signalsfrom the controller, to thereby operate the MGU as either a motor forrestarting the engine or a generator for charging the HV-ESS. In thesecond operating mode, the first switch is opened and the second switchis closed to recharge the LV-ESS.

An electrical system for the vehicle is also disclosed. The electricalsystem includes an HV-ESS, an LV-ESS, a polyphase full-bridge activerectifier/inverter having a DC bus connection point, a first switchpositioned between the DC bus connection point and the HV-ESS, a secondswitch positioned between the DC bus connection point and the LV-ESS, apolyphase MGU electrically connected to AC bus connection points of theactive rectifier, and a controller. The controller includes a processorand memory on which is recorded instructions for controlling theelectrical system to establish a plurality of powertrain operatingmodes. As with the above described vehicle embodiment, the execution ofthe instructions by the processor causes the controller to establish afirst operating mode in which the first switch is closed and the secondswitch is opened via switching signals from the controller to operatethe MGU as either a motor for restarting or assisting the engine, or agenerator for providing power to the HV-ESS and any HV loads, and asecond operating mode in which the first switch is opened and the secondswitch is closed to supply power to the LV-ESS and any LV auxiliaryloads.

The above features and advantages and other features and advantages ofthe present invention are readily apparent from the following detaileddescription of the best modes for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a vehicle having an electricalsystem with a high-voltage motor generator unit (MGU) having amultiplexed output as set forth herein.

FIG. 2 is a schematic circuit diagram of the electrical system of thevehicle shown in FIG. 1 according to an alternative tapped windingembodiment.

FIG. 3A is a schematic circuit diagram of an example embodiment of afull-bridge active rectifier that may be used as part of the electricalsystem of the vehicle shown in FIG. 1.

FIG. 3B is a schematic circuit diagram of an example embodiment of asemi-active rectifier that may be used as part of the electrical systemof the vehicle shown in FIG. 1.

FIG. 4 is a schematic illustration of an alternative portion of theelectrical system of the vehicle shown in FIG. 1 with optional solidstate switches.

FIG. 5A is a schematic illustration of an optional semiconductor switchembodiment usable in lieu of the solid state switches of FIG. 4.

FIG. 5B is a schematic illustration of an alternative embodiment of thesemiconductor switches shown in FIG. 5A.

FIG. 6 is a table describing the various switching states and controlledoperating modes of the systems shown in FIGS. 4-5B.

DETAILED DESCRIPTION

Referring to the drawings, wherein like reference numbers refer to likecomponents throughout the several views, FIG. 1 depicts a schematicexample vehicle 10 having a hybrid electric powertrain 11. Thepowertrain 11 includes an internal combustion engine (E) 12 with acrankshaft 14 that is operatively connected to an input member 16 of atransmission (T) 18. The transmission 18 may include a gearingarrangement and clutches (not shown) through which torque flows from theinput member 16 to an output member 20, and ultimately through a finaldrive 21 to drive wheels 23 of the vehicle 10.

The engine 12 may include a flywheel 25 that rotates in conjunction withthe crankshaft 14. Two different components for starting the engine 12are operatively connectable to the crankshaft 14: an auxiliary startermotor (M) 37 and a polyphase, high-voltage motor generator unit (MGU)36. The auxiliary starter motor 37 is operatively connectable to thecrankshaft 14, e.g., through a gear element 28. A solenoid (not shown)may be selectively energized to engage the starter motor 37 with theflywheel 25 when torque is needed from the auxiliary starter motor 37 tocrank and start the engine 12.

The MGU 36 is also operatively connectable to the crankshaft 14 andoperable for starting the engine 12. In a possible embodiment, the MGU36 may be embodied as an alternating current (AC) electric machinehaving a motor housing or frame 35, with the MGU 36 shown in the Figuresan example three-phase AC electric machine. In various exampleembodiments, the MGU 36 may be constructed as a wound-field synchronousmachine, a wound-field claw pole (Lundell) synchronous machine, apermanent magnet embedded claw pole (Lundell) machine, a permanentmagnet synchronous machine, or a synchronous reluctance machine with orwithout permanent magnets within its rotor. The MGU 36 may also be aninduction machine.

The MGU 36 of FIG. 1 is operatively connected to the crankshaft 14 by adrivetrain 30. The drivetrain 30 may include a belt 38 that engages witha first pulley 40 that is connected to and rotatable with a shaft (notshown) of the MGU 36 and with a second pulley 42 connected to androtatable with the crankshaft 14. Construction and use of the MGU 36 inthis manner is referred to as a belted alternator starter (BAS) system.The MGU 36 in such an embodiment may be powered via a voltage of between24-48 VDC in a non-limiting example embodiment. Alternatively, thedrivetrain 30 may include a chain in lieu of the belt 38, and sprocketsin lieu of the respective first and second pulleys 40 and 42, or anyother suitable drive system.

The hybrid electric powertrain 11 shown in FIG. 1 includes an electricalsystem 13 having a polyphase, full-bridge active rectifier/inverter (AR)39, a high-voltage energy storage system (HV-ESS) 50, anauxiliary/low-voltage energy storage system (LV-ESS) 52, and acontroller (CTRL) 60. The HV-ESS 50 and the LV-ESS 52 may be separateenergy storage devices as shown, or they may be designated portions of asingle battery pack, e.g., a 48 VDC stack with three terminals where thefull stack is used to supply 48 VDC portion and a lower quarter of thestack is used to supply the auxiliary 12 VDC portion.

In some configurations, such as the example embodiments shown in FIGS. 1and 2, the hybrid electric powertrain 11 also includes a polyphase,semi-active auxiliary rectifier (SAR) 44. The embodiment of FIGS. 1 and2 eliminates the DC-DC converter/accessory power module (APM) of theprior art by providing dual-voltage regulation via therectifier/inverter 39 and the semi-active rectifier 44, which may behoused within the frame 35 of the MGU 36 as shown. Such a design mayhelp to reduce system cost, mass, and packaging size.

The MGU 36 of FIG. 1 is electrically connected to the full-bridge activerectifier/inverter 39, and via the rectifier 39 to the HV-ESS 50, via ahigh-voltage DC bus 27, so that the controller 60 can control theoperation of the MGU 36 as a generator or as a motor as needed viaenergy from the HV-ESS 50. The phase windings (W) of the MGU 36 are alsoconnected to the semi-active auxiliary rectifier 44, which is then phasecontrolled via the controller 60 to provide a lower DC voltage outputthan that of the HV-ESS 50. The semi-active auxiliary rectifier 44 iselectrically connected to the LV-ESS 52 via a low-voltage DC bus 127,which in turns supports most of the auxiliary electrical load (L) of thevehicle 10. Although shown separately for illustrative clarity in FIG.1, the electrical load (L) may include the optional auxiliary startermotor 37 shown in FIG. 1.

Referring briefly to FIG. 2, in an alternative tapped windingarrangement the MGU 36 is connected to the full-bridge activerectifier/inverter (AR) 39 and different partial turns (T2, T1) of thephase windings (W). For example, the semi-active rectifier 44 may beconnected to partial turns T2 of the phase windings W, while thefull-bridge active rectifier/inverter 39 is connected to partial turnsT1, with the turn numbers being nominal for the purpose of simplicity.

Key to this particular design is that the active rectifier/inverter 39and the semi-active auxiliary rectifier 44 are electrically connected todifferent turns of the phase windings W of the MGU 36 so as to minimizevoltage stresses and output ripple, particularly of the semi-activeauxiliary rectifier 44. The tapped phase windings (W) in this embodimentare connected to AC bus connection points (AC) of each of the activerectifier/inverter (AR) 39 and the semi-active auxiliary rectifier (SAR)44, with DC bus connection points (DC) connected to the HV-ESS 50 andthe LV-ESS 52 of FIG. 1, respectively.

Referring again to FIG. 1, the controller 60 may be configured as asingle or distributed control device that is electrically connected toor otherwise placed in hard-wired or wireless communication with each ofthe engine 12, the MGU 36, the HV-ESS 50, and the LV-ESS 52, via controlchannels 51. The control channels 51 may include any required transferconductors, for instance a hard-wired or wireless control link(s) orpath(s) suitable for transmitting and receiving the necessary electricalcontrol signals for proper power flow control and coordination aboardthe vehicle 10. The controller 60 may include such control modules andcapabilities as might be necessary to execute all required power flowcontrol functionality aboard the vehicle 10 in the desired manner.

The controller 60 may include a processor 62 and tangible,non-transitory memory 64, e.g., read only memory (ROM), whether optical,magnetic, flash, or otherwise. The controller 60 may also includesufficient amounts of random access memory (RAM), electrically-erasableprogrammable read only memory (EEPROM), and the like, as well as ahigh-speed clock, analog-to-digital (A/D) and digital-to-analog (D/A)circuitry, and input/output circuitry and devices (I/O) 66, as well asappropriate signal conditioning and buffer circuitry.

The configurations of FIGS. 1 and 2 allow for two possible controlmodes: (I) an engine autostart or engine assist mode, and (II) agenerator mode. In mode (I), the MGU 36 is operated as a motordelivering torque to the engine 12 when restarting or assisting theengine 12. The controller 60 uses the active rectifier/inverter 39 as aninverter in mode (I). This includes supplying AC power from the HV-ESS50 for a fast restart or torque assist of the engine 12.

For mode (II), i.e., generator mode, the voltage output of the HV-ESS 50is controlled via the controller 60 by field excitation of the MGU 36,i.e., from the controlled rotation of the engine 12 in combination withphase angle retardation control of the semi-active auxiliary rectifier44. For illustrative clarity, the controller 60 is shown in FIG. 1outside of the frame 35. However, the controller 60 may be furtheroptimized by integrating starter/engine assist/primary control functionsand the auxiliary control function into a single controller within theframe 35 of the MGU 36, along with any power electronics including thefull-bridge active rectifier/inverter 39 and the semi-active auxiliaryrectifier 44.

Example internal detail of the full-bridge active rectifier/inverter 39and the semi-active auxiliary rectifier 44 of FIGS. 1 and 2 are shown inFIGS. 3A and 3B, respectively. In FIG. 3A, the full-bridge activerectifier/inverter 39 may be embodied as a set of semiconductor switches70 electrically connected to the A, B, and C phase leads of the phasewindings (W) of the MGU 36. Each of the semiconductor switches 70 may beconfigured, e.g., as metal-oxide semiconductor field effect transistors(MOSFETs) as shown.

The three terminals of the example MOSFET shown in FIG. 3A are labeledas a gate (G), a source (S), and a drain (D). The controller 60 of FIGS.1 and 2 is configured to selectively activate, i.e., turn on or off, anyof the semiconductor switches 70 as needed via a voltage pulse todelivered to the gate (G), e.g., via the control channels 51 of FIG. 1.Thus, electrical current flowing to or from the MGU 36 is closelycontrolled via precise switching of the various semiconductor switches70. Other embodiments may use other switching devices, for instanceinsulated gate bipolar transistors (IGBTs) or semiconductor-controlledrectifiers (SCRs), for instance solid state AC switches such asthyristors.

The semi-active auxiliary rectifier 44 shown in FIG. 3B, as the nameimplies, is only partially controlled via the controller 60. Unlike thefull-bridge active rectifier/inverter 39 of FIG. 3A, the semi-activeauxiliary rectifier 44 of FIG. 3B has passive control elements in theform of diodes 72 and controllable elements with bidirectional (AC)voltage blocking capability in the form of, for example, SCRs 74. TheSCRs 74 may be embodied as multi-layer, unidirectional current controldevices such as the example thyristors as shown, with each SCR 74 havinga gate (G), an anode (An), and a cathode (C). As is well known in theart, whenever a control voltage applied to the gate (G) and the cathode(C) exceeds a calibrated threshold, which is a quality of the particularthyristor/SCR 74 that is used, the thyristor/SCR 74 is switched on, andthereafter conducts electrical current.

In a thyristor or an SCR, the terms “latching current” refers to thegate trigger current, i.e., a measure of the minimum electrical currentapplied to the gate (G) to ensure the SCR 74 will turn on. The term“holding current” is the minimum current flowing between the anode (An)and cathode (C), after termination of the gate current, needed forensuring that the thyristor/SCR 74 remains on and conducting. Thus, thethyristors/SCRs 74 of FIG. 3B remain on/conducting as long as theconducted current remains at the holding current level. Once the currentflow falls below the holding current for a particular period of timeunique to the design of the thyristor/SCR 74 being used, thethyristor/SCR 74 will switch itself off. If the gate (G) is pulsed andthe current flowing through the thyristor/SCR 74 is below the latchingcurrent, the thyristor/SCR 74 will remain in the off state. Theparticular configuration of FIG. 3B is just one possible example of thesemi-active rectifier 44. For instance, other approaches may reverse thepositions of the diodes 72 and the SCRs 74 in FIG. 3B, such that thediodes 72 are located where the SCRs 74 are shown and vice versa. TheSCRs 74 can be replaced with back-to-back series connected MOSFETs asshown in FIG. 5B with a voltage applied to gate G, and with the source Sused for turning the switch on or off as needed.

The designs depicted in FIGS. 1-3B are able to control a single-frameMGU such as the MGU 36 via the full-bridge active rectifier/inverter(AR) 39 as either a generator or a motor, doing so using high-voltageenergy from the HV-ESS 50. In some embodiments, the HV-ESS 50 may be alithium-ion rechargeable, multi-cell battery pack rated for 48 VDC ormore, or a super-capacitor or ultra-capacitor. A capacitive device maybe suitable for rapid delivery of the necessary cranking current.

As noted above, the phase windings W of the MGU 36 are also connected tothe semi-active auxiliary rectifier (SAR) 44, with the controller 60controlling the phase of the SAR 44 to provide a lower DC voltage outputthan that of the HV-ESS 50. Such an output can be harnessed to rechargeto the LV-ESS 52 or to power the auxiliary electrical load (L). TheLV-ESS 52 in turn can support the auxiliary electrical load (L) wheneverthe engine 12 is stopped. When restarting or providing torque assist tothe engine 12, the MGU 36 is controlled as a motor using the activerectifier/inverter 39 to supply the necessary AC power from the HV-ESS50. The controller 60 can temporarily disable the semi-active auxiliaryrectifier 44 during engine restart or assist so as to ensure thatmaximum torque is made available to the engine 12 by the MGU 36.

Referring to FIG. 4, in an alternative embodiment, the semi-activeauxiliary rectifier 44 of FIGS. 1 and 2 may be eliminated from thedesign. The DC output side of the full-bridge active rectifier/inverter(AR) 39 is connected via the high-voltage DC bus 27 and the low-voltageDC bus 127 to a respective pair of switching devices, i.e., respectivefirst and second switches S1 and S2. In the example embodiment of FIG.4, the switches S1, S2 are both solid-state devices, relays, orcontactors. The HV-ESS 50 and the LV-ESS 52 may be optionally housedtogether in a single battery housing 150, for instance with threeterminals separating a high-voltage stack of 48 VDC from a low-voltagestack of 12 VDC.

Referring briefly to FIGS. 5A and 5B, in another possible embodiment theswitches S1, S2 may be configured as semi-conductor switching devices,e.g., IGBTs or MOSFETS as shown, which may be optionally integrated intothe frame 35 of the MGU 36 or, alternatively, into the HV-ESS 50 andLV-ESS 52. In FIGS. 5A and 5B, the gate, drain, and source are labeledas G, D, and S, respectively. The switches S1, S2 are oriented toprovide the output multiplexing function in a generator mode. When thegate signal to the first switch S1 is disabled by the controller 60, thehigh-voltage DC bus 27 is isolated when voltage from the MGU 36 ingenerator mode is reduced to match that of the low-voltage DC bus 127.Likewise, when the gate signal to switch S2 is disabled by thecontroller 60, the low-voltage DC bus 127 is isolated when the voltagefrom the MGU 36 in generator mode is raised to the level of thehigh-voltage DC bus 27.

The optional embodiment of FIG. 5B illustrates a series back-to-backconnection of MOSFETS in the first switch S1 to block current flow inboth directions when the first switch S1 is turned off. Although omittedfor simplicity, the switch S2 may be configured in the same manner. Sucha configuration may help to prevent an unintended discharge of powerfrom the HV-ESS 50 or LV-ESS 52 during certain types of electricalfaults.

Referring to FIG. 6, a table 80 depicts possible switching states andresultant control modes for the optional design shown in FIG. 4. Duringmotoring and regeneration of the HV-ESS 52, as indicated by M/REG inFIG. 6, the switching device S1 is closed/switched on (X) and S2 isopened/switched off (O) by the controller 60. As the second switch S2connects the DC bus of the active rectifier/inverter 39 to the positiveside of the low-voltage DC bus 127, this particular switching actioneffectively disconnects the LV-ESS 52 of FIG. 4 from the activerectifier/inverter 39.

During regeneration of the LV-ESS 52, the first switch S1 is commandedto open by the controller 60 and the switching device S2 is commanded toclose. As the first switch S1 connects the DC bus of the activerectifier 39 to the positive side of the high-voltage DC bus 27, thisswitching action disconnects the HV-ESS 50 from the activerectifier/inverter 39. In this embodiment, the LV-ESS 52 of FIG. 4provides a stable voltage to the auxiliary electrical load (L) duringengine auto-start/assist and regeneration modes. Excitation of the MGU36 may be reduced for low-voltage regeneration, and enhanced forhigh-voltage regeneration or when restarting of or providing torqueassist to the engine 12.

The disclosed design of FIGS. 1-6 is intended to provide low-cost enginebelt-driven start/stop operation with torque boost and braking energyregeneration capability. The conventional DC-DC converter typically usedfor a dual-voltage electrical system is eliminated, thereby reducingsubstantial cost and mass. The system disclosed herein also reducespackaging space and integration costs associated with use of the DC-DCconverter, while reducing controller costs via integration ofstarter/primary voltage control function and the auxiliary voltagecontrol function into a single controller.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternate designs and embodiments for practicingthe invention within the scope of the appended claims.

The invention claimed is:
 1. A vehicle comprising: an internalcombustion engine having a crankshaft; a transmission having an inputshaft that is connected to the crankshaft; an auxiliary electrical load;a high-voltage (HV) electrical load; a drivetrain; and an electricalsystem that is characterized by an absence of a direct current (DC)-DCconverter, and that includes: a high-voltage energy storage system(HV-ESS) that is electrically connected to the HV electrical load; alow-voltage energy storage system (LV-ESS) that is electricallyconnected to the auxiliary electrical load; a polyphase full-bridgeactive rectifier/inverter having a plurality of semiconductor switches;a polyphase semi-active auxiliary rectifier; a polyphase motor generatorunit (MGU) having phase windings that are electrically connected to theHV-ESS via the active rectifier/inverter and to the LV-ESS via thesemi-active auxiliary rectifier, wherein the MGU is operativelyconnected to the crankshaft via the drivetrain; and a controllerconfigured to selectively execute a first operating mode in which thesemi-active bridge rectifier is temporarily disabled and the MGU isoperated as a motor to restart or assist the engine, wherein the firstoperating mode includes supplying alternating current (AC) power to thephase windings of the MGU using an output of the full-bridge activerectifier/inverter, and a second operating mode in which the MGU isoperated as a generator such that the full-bridge activerectifier/inverter supplies DC power to the HV-ESS and to the HVelectrical load, and in which the semi-active auxiliary rectifierprovides an auxiliary direct current (DC) output voltage to the LV-ESSand to the auxiliary electrical load.
 2. The vehicle of claim 1, whereinthe auxiliary electrical load includes an auxiliary starter motor. 3.The vehicle of claim 1, wherein the drivetrain includes a first pulleyconnected to and rotatable via the MGU, a second pulley connected to androtatable via the crankshaft, and a belt that engages the first pulley.4. The vehicle of claim 1, wherein the polyphase semi-active auxiliaryrectifier includes a plurality of diodes and a plurality of thyristorsin communication with the controller.
 5. The vehicle of claim 1, whereinthe full-bridge active rectifier/inverter and the semi-active auxiliaryrectifier are electrically connected to different turns of the phasewindings of the MGU.
 6. The vehicle of claim 1, wherein the HV-ESS andthe LV-ESS are housed together in a single battery housing.
 7. Thevehicle of claim 1, wherein the MGU has a single frame, and wherein thefull-bridge active rectifier/inverter and the semi-active auxiliaryrectifier are housed within the single frame.
 8. An electrical systemfor use with an internal combustion engine, a transmission, ahigh-voltage (HV) electrical load, and an auxiliary electrical load, theelectrical system comprising: a high-voltage energy storage system(HV-ESS); an auxiliary/low-voltage energy storage system (LV-ESS) thatis electrically connected to the auxiliary electrical load; a polyphasefull-bridge active rectifier/inverter having a DC bus connection point;a polyphase motor generator unit (MGU) electrically connected to thefull-bridge active rectifier/inverter via an AC bus connection point;and a controller having a processor and memory on which is recordedinstructions for controlling the electrical system to establish aplurality of powertrain operating modes, wherein execution of theinstructions by the processor causes the controller to establish a firstoperating mode, via signals from the controller, to operate the MGU as amotor for restarting or assisting the engine, and a second operatingmode in which auxiliary power is delivered to the LV-ESS and theauxiliary electrical load; wherein the electrical system ischaracterized by an absence of a DC-DC converter.
 9. The electricalsystem of claim 8, further comprising a first switch positioned betweenthe DC bus connection point and the HV-ESS and a second switchpositioned between the DC bus connection point and the LV-ESS, whereinin the first operating mode the first switch is closed and the secondswitch is opened, and wherein in the second operating mode the firstswitch is opened and the second switch is closed.
 10. The electricalsystem of claim 9, wherein the first and second switches aresemiconductor switches.
 11. The electrical system of claim 10, whereinthe semiconductor switches are arranged in a series back-to-backconfiguration.
 12. The electrical system of claim 9, wherein the firstand second switches are contactors or relays.
 13. The electrical systemof claim 9, wherein the MGU has a single frame, and wherein the activerectifier/inverter and the first and second switches are housed withinthe single frame.
 14. The electrical system of claim 8, furthercomprising a polyphase semi-active auxiliary rectifier, wherein thephase windings of the MGU are electrically connected to the LV-ESS viathe semi-active auxiliary rectifier.